For over thirty years motorcycles have typically included forked rear swing arm suspension systems. In such systems the rear wheel is journalled to the end of a forked swing arm. The forward end of the swing arm is hinged to the motorcycle body at a point forward of the wheel, and extends rearwardly therefrom. The swing arm is spring-loaded and damped, so as to absorb weight loads and road shocks by undergoing limited swinging motion in a vertical plane.
Some touring motorcycles have a pair of spring-loaded shock absorbers which extend upwardly from the ends of the forked swing arm. In such systems weight loads and road shocks are transmitted almost directly from the wheel axle to the shock absorbers. Most modern motorcycles, however, particularly including the off-road, or "motocross" motorcycles, have a single shock absorber and spring assembly, which is located forward of the wheel. In such systems weight loads and road shocks are transmitted through the swing arm to the shock absorber.
In recent years there has been introduced at least one class of one-sided rear swing arm assemblies. In these assemblies the rear wheel is journalled to an axle that extends horizontally in a cantilevered manner from the end of the swing arm, with the swing arm extending around and alongside one side of the wheel. Such an arrangement facilitates changing of the rear wheel, which can be removed horizontally from the free end of the axle, and also results in lighter overall weight, greater rigidity, and other advantages.
A problem associated with the previously known one-sided rear swing arm assemblies is that it has been difficult to provide a satisfactory mechanism for adjusting the tension in the drive chain. It will be recognized that in conventional forked swing arm assemblies this is not a problem, as the chain tension is readily adjusted by sliding the wheel forwardly or rearwardly in the slots which are ordinarily employed for engaging and supporting the axle of the wheel, and which are elongated for the purpose of allowing for adjustment of the chain tension. However, in the one-sided swing arm assemblies this approach has not been feasible.
Consequently, one approach has been to journal the rear wheel in an eccentrically mounted journal bearing, which can be selectively rotated to adjust the chain tension. Although this mechanism accomplishes the purpose of adjusting the chain tension, it also necessarily results in the rear wheel being raised or lowered with respect to the rest of the motorcycle, resulting in a small but definite change in ride height when the chain tension is adjusted.
The applicant has previously disclosed and claimed a one-sided front wheel suspension system in his U.S. Pat. No. 4,526,249, issued on Jul. 2, 1985, which is hereby incorporated by reference. As will be appreciated from the description below of the present invention, some of the same advantages that are obtained in the one-sided front wheel suspension system are also obtained in the rear wheel suspension system of the present invention. For example, in a one-sided suspension system weight loads and road shocks are transmitted to points on the motorcycle body which are both low, that is, close to the ground, and close to the center of gravity of the motorcycle, with consequent improvement in the handling, performance and ride of the motorcycle. Also, in a one-sided suspension system weight loads and road shocks are transmitted in a more direct path to the motorcycle body, thereby permitting a net reduction in the size and weight of the load-bearing structures that transmit these loads to the motorcycle body.